Fire detector element



Feb. 19, 1952 PETERS 2,586,252

FIRE DETECTOR ELEMENT Filed May 2. .1949

INVENTOR. A14] Z-ZVflZZEF i $745 25 Patented Feb. 19, 1952 FIRE DETECTOR ELEMENT Melville F. Peters, East Orange, N. J., assignor to Petcar Research Corporation, Newark, N. J a corporation of New Jersey Application May 2, 1949, Serial No. 90,881

6 Claims.

curs. More particularly, the invention has to do with that class of such devices which operate on an increase, to some predetermined value, in the ambient temperature within the monitored space and applied to a part of the system or device, as distinguished from fire detecting devices which are caused to operate by the light emitted by a flame, or by the efiect of smoke on a, photoelectric cell, or in other known manner.

The invention consists in the provision of a fire detector in the form of a readily bendable tubing of indefinite continuous length having Within it and spaced from it and from each other two continuous uninsulated electrically conductive wires which are maintained in spaced relation to each other and to the surrounding tubing by a discontinuous element which fills the tubing and surrounds and engages the conductors and which is formed of a material which is nonconductive to electricity at normal temperatures but becomes electrically conductive at some predetermined abnormal temperature such as that of the combustion of some selected material. The two conductors are connected in an alarm or signal system which is closed to operate the signal or alarm by completion of the circuit between the two conductors when the normally non-conductive material becomes conductive on heating.

Other results, advantages and new features of my invention will be'made apparent by the description and drawings forming part hereof but which are solely for the purpose of describing one embodiment of my invention and therefore impose no limitation on the invention not specfically stated in the claims.

In the drawings,

Fig. '1 illustrates part of an airplane, showing a fire detector element'led through parts thereof;

Fig. 2 illustrates a detector element according to this invention included in the circuit of an electric fire detection system;

Fig. 3 illustrates part of a fire detector element according to this invention, part of the protective casing being broken away, and part of one of the beads being broken away;

Fig. 4 is a sectional view taken on line 4-4 of Fig. 3, and

Fig. 5 is a cross-sectional view similar to Fig. 4 but showing a modified form of the invention.

In Fig. 1 of the drawings there is shown, for illustration only, how a continuous fire detector element such as that provided by the invention may be employed to monitor a space in which fire may occur. The fire detector element 2 is here shown as being led through the engine nacelle 4, wings 8, 8 and fuselage 9 of an aircraft and, upon undesired increase in the ambient temperature at any point along the length thereof, will 0perate in the manner described hereinafter to operate a signal or alarm II providing a warning to the pilot. Obviously any other type of structure or space, such as a room, baggage hold, etc., may be monitored with the same apparatus and with the same results.

The fire detector element 2 is shown in Figs. 2, 3 and 4 and comprises a readily bendable tube In of indefinite continuous length within which are two spaced, parallel, electrically conductive wires [2, I4 which are surrounded, supported and held permanently in spaced relation to each other and to the tubing ill by a discontinuous element I3 filling the tube throughout its length and consisting, in effect, of a plurality of separate beads I 6 which are formed on and fused to the conductors, are spaced along the length thereof, and which are of such size as to fill the tubing. The conductors l2, l4 are preferably made of stainless steel or Inconel but may be formed of other suitable material. The protective casing is may be formed of Inconel which is an excellent heat conductor and has been found to give good results.

The discontinuous element which supports and spaces the two conductors is made of a material which is electrically non-conductive at normal temperatures but which becomes electrically conductive at some abnormal high temperature, such as the temperature of combustion of gasoline. The beads of this element may be fused to the conductors in any satisfactory manner but are preferably formed and fused to the conductors by the method disclosed and claimed in my copending application Serial No. 2,344, filed January 14, 1948, for Fire Detector Element, now Patent No. 2,495,867, dated January 31, 1950, and in the drawing they are shown as they are actually formed by such method. In such a method, the two conductors are encased in a cylinder of thermistor material which includes an inert ceramic ingredient such as steatite and an ingredient which is removed by heating. Alternatively, the cylinder may comprise thermistor material together with the inert ceramic compound, the thermistor material taking the form of one or more metallic organic compounds which dissociate on heating. In either event, when the cylinder is subjected to heat, the ceramic material shrinks into the form of closely spaced beads, which firmly adhere to the conductors to provide good contact therewith. The small spacing between adjacent beads permits the beads to accommodate themselves to bending of the casing about small or large radii while at the same time the beads cover the greater parts of the lengths of the two wires. The tubing and beads are pref erably circular in cross-section but may be made elliptical, in which case the wires are placed within the major axis of the beads as clearly shown in Fig. 5.

In an embodiment of the invention which has been constructed and is operated successfully, two Inconel conductors, each of which is .010 inch in diameter, are embedded in beads having an out side diameter of .050 inch. In this element the conductors are spaced .010 inch wall to wall, and the minimum distance between the periphery of each conductor and the outer surface of the beads is .010 inch. Such an element is so thin that it may be bent on very small radii without difficulty and without danger of breaking the conductors or loosening them from the surrounding beads. If the spacing of the wires is materially increased above that stated above it may be desirable, but perhaps not necessary, to make the tubing and beads elliptical in cross-section, placing the conductors in the major axis of the cross-section, as shown in Fig. 5. In such an embodiment of the invention, the elliptical beads may have exterior dimensions of '.060 inch and .040 inch, and the conductors may be .010 inch in diameter. By making the beads elliptical in cross-section resistance to bending about any axis other than one parallel to the major axis is created and in all normal, unforced bending of the elliptical detector element only such bending will take place, thus insuring equal bending of the conductors.

As illustrated in Fig. 2 the conductors 12, I4 of the detector element may form part of an electric circuit including battery 30, signal 32 and test switch 34. In normal operation and use the test switch is left open and the signal 32 is therev fore normally de-energized. If any part of the element, for example part A, is subjected to a predetermined temperature which may be that of combustion of gasoline, the electrical resistance of the material of which the beads are formed is so reduced that electric energy flows through the bead or beads, and thus between the two conductors, at location A, completing the circuit through battery 30, signal 32 and those parts of the conductors l2, 14 between location A and the battery and signal, thus energizing the signal. When the predetermined temperature at location A is removed, for example by putting out the fire, the resistance of the beads will revert to its normal high value and no current will flow in the alarm circuit. The enclosing and protective tube l may or may not be grounded. In either case small parasitic currents will flow between each conductor and the tube on operation by heating but these will not in any way affect the operation of the device or the system.

The term normal temperature is used herein as defining a temperature lower than that which is generally known in the art as flame temperature, and the term abnormal temperature, as defining flame temperature or a temperature higher than the same.

While I have described and illustrated but one embodiment of the invention, it will be apparent to those skilled in the art that other embodiments, as well as modifications of those disclosed, may be made without departing in any way from the spirit or scope of the invention, for the limits of which reference must be made to the appended claims.

What is claimed is:

1. A readily bendable cable-like element of indefinite continuous length for use in the detection of abnormal temperature conditions at any location along its length, comprising a bendable tubing element formed of material of relatively high heat conductivity, a unitary assembly disposed within and tightly fitting the tube but being sepa' rate therefrom and comprising two electrically conductive uninsulated wires which are substantially co-extensive in length with the tubing element and are spaced therefrom and from each other throughout their length, and a discontinuous member formed of a material which is substantially non-conductive to electricity at normal lower temperatures and which becomes conductive to electricity at abnormalhigher temperatures surrounding and adhered to said wires and which maintains them in closely spaced relation to each other and tightl engages the interior surface ofthe tubing element to provide an electrically conductive path between the wires in substantially instantaneous response to abnormal higher ambient temperatures to which the exterior of the tubing element may be subjected, while electrically insulating the wires from each other at normal temperatures.

2. An element according to claim 1, in which the tubing element and the assembly'therein are circular in cross-section.

3. An element according to claim 2, in which the diameter of each wire is approximately .010 inch, the spacing of the wires is approximately .010 inch and the diameter of the unitary assembly is approximately .050 inch.

4. An element according to claim 1, in which the tubing element and the assembly therein are elliptical in cross-section.

5. An element according to claim 4, in which the diameter of each wire is approximately .010 inch, the spacing of the wires is approximately .010 inch and the exterior dimensions of, the unitary assembly are .060 inch by .040 inch.

6. A readily bendable cable-like element of indefinite continuous length for use in the repeated detection of abnormal temperature conditions at any location along its length, comprising a bendable tubing element formed of material of relatively high heat conductivity, a unitary assembly disposed within and tightly fitting the tube but being separate therefrom and comprising two electrically conductive uninsulated wires which are substantially co-extensive in length with the tubing element and are spaced therefrom and from each other throughout their length, and a discontinuous member formed of a material which is not changed in physical state when subjected to the abnormal temperatures which are to be detected, which is substantially non-con ductive to electricity at normal lower temperatures, and which becomes conductive to electricity at abnormal higher temperatures, surrounding and adhered to said wires and which maintains them in closely spaced relation to each other and tightly engages the interior surface of the tubing element to provide an electrically conductivepath between the wires in substantially instantaneous 5 response to abnormal higher ambient temperatures to which the exterior of thetubing element may be subjected, while electrically insulating the wires from each other at normal temperatures.

MELVILLE F. PETERS.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number Name Date Dahlstrom May 17, 1932 Siddall et a1. Oct. 5, 1937 Pearson et a1 Aug. 26, 1941 Grisdale Oct. 14, 1941 Walbridge Dec. 24, 1946 Postal July 26, 1949 Peters Jan. 31, 1950 FOREIGN PATENTS Country Date Norway Mar. 24, 1947 

